Field of the Invention
The present invention relates to a measurement device.
Priority is claimed on Japanese Patent Application No. 2014-051557, filed on Mar. 14, 2014, the contents of which are incorporated herein by reference.
Description of Related Art
A measurement device generally includes a sensor configured to detect a physical quantity (e.g., temperature, pressure, flow rate, or the like) and a signal processor configured to process a detected signal detected by the sensor. The signal processor converts the detected signal obtained from the sensor into a digital signal and performs a predetermined calculation processing for the digital signal to measure a physical quantity. Such a measurement device includes a device configured to measure a physical quantity while performing internal calibration to prevent degradation of measurement accuracy due to a measurement error. The measurement error is caused by aging or the like.
In particular, the measurement device capable of performing internal calibration sequentially converts a detected signal obtained from the sensor and a calibration signal previously prepared into a digital detected signal and a digital calibration signal, respectively. Then, the measurement device performs a predetermined calculation processing using the digital detected signal and the digital calibration signal to correct a measurement error and to measure a physical quantity with a high degree of accuracy. The above-described calibration signal is for calibrating a zero-point (e.g., a lower limit in a signal range), a span (e.g., a difference between an upper limit and a lower limit in a signal range), or the like, or for indicating internal terminal temperature or the like. Such a measurement device is provided in, for example, a field device used in an instrumentation system, various recorders (for example, a paperless recorder and a chart recorder), a data logger, or the like.
Japanese Patent Application Laid-Open Publication No. 2011-220698 (hereinafter, referred to as “PTL1”) discloses a multipoint switching measurement device capable of measuring analog signals of a plurality of channels while performing the above-described internal calibration. In particular, the multipoint switching measurement device disclosed in PTL 1 shortens the update cycle of a specific channel measurement, while increasing an update cycle of another channel measurement. Thereby, the multipoint switching measurement device enables the measurements of all channels.
The above-described measurement device capable of performing internal calibration includes a main controller configured to integrally control operations of the measurement device. The main controller sequentially performs a control for converting a detected signal obtained from the sensor into a digital signal and a control for converting a calibration signal into a digital signal. Therefore, the measurement device in the related art sequentially and repeatedly performs a first process for converting a detected signal obtained from the sensor into a digital signal based on instructions of the main controller, a second process for converting a calibration signal into a digital signal based on instruction of the main controller, a third process for calculating measured results using the digital signals obtained by the first and second processes. In other words, the measurement cycle in the measurement device in the related art is from a time when the above-described first process is started to a time when the third process is completed and the main controller obtains the calculation results of the third process.
Recently, an increase in the speed of a measurement device is in demand, thus, shortening of a measurement cycle is desired. Since the above-described measurement device in the related art sequentially performs the above-described first to third processes by sequentially performing the control for converting a detected signal obtained from the sensor into a digital signal and the control for converting a calibration signal into a digital signal using the main controller, there are some cases where the shortening of the measurement cycle is difficult. In addition, the above-described measurement device in the related art is required to perform both the control for converting a detected signal obtained from the sensor into a digital signal and the control for converting a calibration signal into a digital signal in the measurement cycle. In other words, the above-described measurement device in the related art is required to perform the communication with regard to a control signal twice in the measurement cycle. This contributes to an increase in the measurement cycle.